Addition agent for acid copper electrolytes



p 1962 R. E. HARROVER, JR 3,054,734

ADDITION AGENT FOR ACID COPPER ELECTROLYTES Filed Sept. 9, 1960 F i g. l

Acid Copper Electrolyte Plus on Addition Agent Fig.2.

A B F E Cathodic Cathodic 2 E D D u u "2 *2 2 5 t+ C D a X- Plating TtmeX Plating Time I Y Y Between I00 Seconds and Sec. BetweenlOOsecondsundfi sec/ Y- Depicting Time at least f X WITNESSES INVENTOR 91A(M, Robert E. Horrover, Jr. 9 MMM itg 3,054,734 ADDITIGN AGENT FOR ACIDCOPPER ELECTROLYTES Robert E. Harrover, In, North Huntingdon Township,

Westmoreiand County, Pa, assignor to Westinghouse Electric Corporation,East Pittsburgh, Pa, a corporation of Pennsylvania Filed ept. 9, 1960,Ser. No. 54,893 Claims. (Cl. 20452) This invention relates to theelectrodeposition of cop per from acid electrolytes embodying certainaddition agents to promote smoother, more ductile electrodeposits ofcopper.

The electrodeposition of copper from acid copper electrolytes oftenresults in an electrodeposit that is rough, spongy, dark colored orotherwise unsuited for the purpose for which it is intended. Manyaddition compounds have been proposed for incorporation in acid copperelectrolytes for the purpose of providing improved deposition of copperon articles therefrom. The addition compounds are often referred to inthe art as addition agents.

This invention is directed to a plating bath comprising copper sulfateand sulfuric acid, and containing in solution a relatively small amountof mercury.

For a complete understanding of this invention, reference is made to thefollowing description taken in conjunction with the accompanyingdrawing, in which:

FIGURE 1 is a sectional view in elevation of apparatus suitable fordirect-current electroplating; and

FIG. 2 is a graph illustrating one type of periodic reverse currentelectroplating.

In accordance with this invention it has been discovered thatfine-grained, ductile electrodeposits of copper can be obtained by theaddition of mercury to an acid electrolyte plating bath comprisingcopper sulfate and sulfuric acid. Furthermore, the brightness andsmoothness of the copper electrodeposit is enhanced substantially byemploying mercury in conjunction with some of the socalled brighteningaddition agents.

The mercury can be added in the form of mercurous or mercuric compounds.The mercurous and mercuric compounds can be either organic or inorganic.The mercury compounds employed in carrying out this invention must besoluble in the acid copper electrolyte in an amount sufiicient toproduce appreciable results.

The concentration of mercury in the bath can be in the range of fromabout 0.0003 to 0.01 ounce per gallon of electrolyte. As used in thisspecification and in the appended claims the quantities given formercury refer to quantities calculated as the metal.

Suitable mercury compounds for use in this invention include mercuricacetate, mercuric benzoate, mercuric formate, mercuric oxalate, mercuricsulfate, p-acetoxy- .lElCLlllC aniline, mercurous sulfate, mercurousacetate, mercurous fluoride, and p-aminophenylmercuricacetate.

The mercury can be used as the sole addition agent in acid copperelectroplating baths if desired. It is preferred, however, to employ themercury in conjunction with certain brightening agents as the mercuryalone has no appreciable effect on the brightness of the copperelectrodeposit. It has been determined that mercury, in the range ofconcentration above set forth, and in conjunction with known brighteningaddition agents does improve substantially the brightness and smoothnessof the copper electrodeposit over that obtained by using the knownbrightening addition agents alone. Further, the mercury addition of thisinvention will extend substantially the useful life of most availablebrightening agents.

Thus, for example, mercuric sulfate can be added to a series of acidcopper baths containing such brightening agents as phenyl sulfonic acid,thiourea, N-acetyl thiourea,

3,054,734 Patented Sept. 18, 1962 N-propionyl thiourea,N-trifiuoroacetyl thiourea, N-pentafiuoropropionyl thiourea, N-furfuroylthiourea, dimethyl thiourea, and cyanoacetyl thiourea. The brightness ofthe electrodeposit is improved substantially over the use of any one ormore of the above brightening agents without the mercury addition.smoothness and ductility of the copper electrodeposit is improvedsubstantially also.

Additionally, the mercury addition agent of this invention can beemployed in combination with the brightening addition agents disclosedin U.S. Patent No. 2,700,019, assigned to the assignee of the presentinvention.

The addition agents disclosed in Patent 2,700,019 are employed inamounts of from about 0.0005 to 0.05 ounce per gallon of electrolyte andcomprise 2-thiohydantoin and certain derivatives of 2-thiohydantoinhaving the following thiohydantoin structure 2 0 II S and having atleast one organic substituent in any one of the 1, 3, and 5 positions.Various organic radicals can be substituted at any one or more of the 1,3, or 5 positions, as long as the compound is not rendered so insolublethat it Will not dissolve in the acid copper electrolyte in an amountsufiicient to produce an appreciable result. Examples of suitablecompounds include 1-acetyl-2-thiohydantin,5(2-hydroxylbenzal)-2-thiohydantoin, S-furfural-2-thiohydantoin,'1-benzol-2-thiohydantoin, S-benzol-2-thiohydantoin,l-methyl-Z-thiohydantoin, and 3- acetyl-Z-thiohydantoin. r

The mercury addition agent of this invention can be used also incombination with the addition agents disclosed in U.S. Patent No.2,853,443 to Robert E. Harrover, Jr., assigned to the assignee of thepresent invention.

The compounds disclosed in Patent 2,853,443 are employed in acid copperelectroplating baths in amounts of from about 0.0001 to 0.5 ounce pergallon of electrolyte and are obtained by admixing and heatingsubstantially equimolar proportions of at least one compound having thenucleus tilt and at least one alkylolamine selected from the groupconsisting of primary, secondary and tertiary alkylolamines in which thegroups substituted on the nitrogen atom are selected from the groupconsisting of hydrogen, alkyl groups, and alkylol groups having from 1to 4 carbon atoms, there being at least one alkylol group per molecule.

Examples of suitable compounds having the nucleus -C-NO II I ll 0 H stit 3 and other suitable alkylolamines. Reference is made also to Patent2,853,443 for the method of reacting the above compounds to provide thedesired reaction product.

The mercury addition, in accordance with this invention, can be employedalso in conjunction with the brightening agents disclosed in applicationSerial No. 770,775, filed October 30, 1958, to enhance substantially thebrightening effect of the disclosed addition agents. Application SerialNo. 770,775, now US. Patent 2,997,428, is assigned to the assignee ofthe present invention.

In application Serial No. 770,775, there are disclosed novel reactionproducts which, when employed in acid copper electroplating baths inamounts of from about 0.001 to 0.5 ounce per gallon of electrolyte,improve the brightness of the copper electrodeposit.

In preparing the novel reaction products disclosed in application SerialNo. 770,775, any of the several compounds having the nucleus C-NC U H Hs can be reacted with ammonia or cetrain derivatives thereof as will bedescribed more fully hereinbelow. An example of a particularly suitablealiphatic compound having the nucleus GNC tit

Examples of other compounds, having the nucleus -C-NC is acetylthiourea.

are Z-thiohydantoin and substitution derivatives of Z-thiohydantoinhaving at least one organic substituent in the l, positions. The nucleusof these Z-thiohydantoin substituent derivatives has the followingstructure:

Various organic radicals can be substituted at one or both of the 1 or 5positions, providing the resultant compound obtained upon reaction withammonia or derivatives thereof is soluble in the acid copper electrolytein an amount sufiicient to'produce an appreciable improvement inbrightness and smoothness of the copper deposited. Examples of suitablecompounds are:

Z-thiohydantoin -1-acetyl-2-thiohydantoin .5 (Z-hydroxylbenzal)-2-thiohydantoin 5 -furfural-2-thiohydantoin -5-benzal-2-thiohydantoin-.1-methyl-2-thiohydantoin Various organic radicals can be substitutedfor hydrogen at any one or more of the 1, 5 or 6 positions, providingthe resultant compound obtained upon reaction with the ammonia orderivatives thereof is soluble in the acid electroplating bath. Examplesof suitable compounds of this nature include:

Compounds which can be reacted with compounds having the nucleus lllllOHS to form the addition agents disclosed in application Serial No.770,775 comprise compounds selected from the group consisting of (A)monocyclic unsubstituted aromatic compounds containing in the ringstructure from 4 to 6 carbon atoms and from 1 to 2 nitrogen atoms permolecule and (B) compounds having the formula wherein R is a radicalselected from the group consisting of hydrogen; monovalent and divalentsaturated aliphatic hydrocarbon radicals having from 1 to 4 carbon atomsand in which the substitutents are NH radicals; monovalent and divalentalicyclic radicals containing from 5 to 6 carbon atoms in the ring inwhich the substituents are selected from the group consisting of CH andNH radicals; monovalent and divalent heterocyclic radicals having from 5to 6 carbon atoms in the ring and in which hetero atoms occur only inthe ring structure and the substituents occur only in the carbon atomsand are NH radicals; phenyl radicals; and aminophenyl radicals.

Specific examples of compounds included within the scope of the termsidentified as (A) and (B) above include: ammonia, isopropylamine,ethylenediamine, dibutylarnine, methylpropylenediamine,diethylenediamine, cyclopentylamine, dicyclohexylamine,cyclopentylmethylamine, cyclopentylethylenediamine,B-methylcyclohexylamine, 1,2-diaminocycl0pentane, Z-aminothiazol,3,5-diamino 1,2,4 triazole, aniline, p-aminoaniline, methylaniline,methyl-2-aminothiazole, 3-methylamino-5-amino- 1,2,4-triazole,2-cyclohexylaminothiazole, ethyl-4-methylcyclohexylarnine,4-cycloheXylamino-5amino-2-pyridine,

4 methylaminocyclohexylamine, p-aminomethylaniline,

3,3'-diisothiazolylamine, cyclohexylaniline, Z-methylcyclohexylthiazol2, diphenylamine, 3 amino-S-phenylamino-1,2,4-triazole thiazolyl 2phenylamine, pyridine, pyrimidine, pyrazine,phenyl-4-aminocyclohexy1amine, 4- methylcyclohexylpropylenediamine, N-(ZthiazolyD-paminoaniline, dimethylcyclohexylamine, phenylethylenediamine,di 4 aminocyclohexylamiue, N-cyclopentylaminoaniline, 3 (2'thiazolylamino)-5-amino-l,2,4-triazole, phenyl-p-aminoaniline,Z-thiaZolylethyIenediamine,

3-p-aminophenyl-5-amino-1,2,4-triazole, N(2-aminoethylene)-l,4-diaminocyclohexane,N-cyclopentyl-1,4-diaminocyclohexane, cyclohestylmethylcyclohexylamine,N- (2' thiazolyl)-1,2-diminocyclopentane, di-p-aminophenylamine, paminophenyl 4 methylcyclohexylamine, 4-methylcyclohexylphenylamine,p-arninophenylethylenediamine, p-aminophenyl-3-aminocyclopentylamine, N-(2-aminoethylene) -3 ,5 -diaminopyridine, N-(3-amino-1,4- thiapyranyl 5)4-methylcyclohexylamine, N (3'- methylcyclopentyl) l,4-diaminocyclohexane, N- 3'-methylcyclohexyl) -4-aminocyclohexane, 3-aminocyclohexyl- 3-aminopyridyl-5-amine and di-2-amino-l,4-pyranyl-4-amine.

The following specific examples illustrate the preparation of the noveladdition compounds disclosed in application S.N. 770,775.

Example I About 1 mol of l-acetyl-2-thiohydantoin and one mol of ammonia(28% aqueous solution) are dissolved in three liters of ethanol andplaced within a suitable reaction vessel. The resultant solution then isheated to boiling and refluxed for about 30 minutes. The solution thenis evaporated to about one liter in volume. The resultant product is aviscous slurry. It is cooled, filtered, and the separated crystals areair dried. The reaction product is a light brown, crystalline solidwhich darkens to a reddish brown on exposure to air. This reactionproduct, when added to acid copper plating baths, brings about animproved brightness in copper electrodeposited therefrom.

Example 11 One mol of acetylthiourea is dissolved in 1.1 mols ofn-propyl amine by heating the components in a suitable reaction vessel.Upon cooling, a solid reaction product crystallizes from the solution.The product obtained upon air drying is a white crystalline masssuitable for addition to an acid electrolyte for the purpose of bringingabout improved brightness of metal electrodeposited therefrom. Theproduct has a melting point of 170 173 C. The melting point of thisproduct when admixed with acetylthiourea, is 126 C.

Reference is hereby made to application S.N. 770,775, filed October 30,1958, for a complete description of the above addition compounds and themethod of preparing the same.

It has been determined that in certain plating baths improved resultsare obtained by incorporating a minor amount of chlorides, present as achloride ion, in the plating bath with the known brightening additionagents described thereinabove. Commercial hydrochloric acid (37%) can beused for this purpose to provide from about 0.001 ounce per gallon to0.06 ounce per gallon of chloride ion component depending upon thequantity of the addition agent introduced into the plating bath. Usuallythe amount of chloride ion component present will not exceed about 0.03ounce per gallon. Alkali metal chloride such as sodium chloride, calciumchloride and other ionizable chloride salts can be added to introducethe chloride ions into the electrolyte.

The chloride ion in proper concentration removes the low current densitydiscoloration that results when many of the presently availablecommercial brightening agents are employed in the bath. In accordancewith the prior art teachings the chloride concentration is critical andmust be carefully controlled. If excessive amounts of chloride ion arepresent in the bath, the efiect of the brightening agent employed isnullified substantially, and the copper electrodeposit will become dulland coarse grained.

It has been determined that when mercury is added to the plating bath inthe amounts hereinabove defined and in accordance with this invention,the concentration of the chloride ion needs not be so carefullycontrolled as '6 above set forth. This is an important advantage to theelectroplating art as it is presently practiced, since the chlorideconcentration is often increased inadvertently by drag-in from precedingelectrolytes and acid dips.

Thus, for example, when the chloride ion concentration is about 0.03ounce per gallon in acid copper baths containing certain brighteners,the copper electrodeposit will often have a dull flat appearance. Afterthe mercury addition in accordance with this invention, the copperelectrodeposit takes on its desired bright appearance.

Acid copper electrolytes suitable for plating copper are well known.Ordinarily, such electrolytes comprise an aqueous solution havingdissolved therein from 20 to 40 ounces per gallon of copper sulfate andfrom 1.3 to 13 ounces per gallon of sulfuric acid. In industry at thepresent time, one widely used acid copper plating bath comprises asolution of 28 ounces per gallon of copper sulfate crystals and 8 ouncesper gallon of sulfuric acid (98% Mercury in the desired amount is addedto the bath in the form of a soluble mercury compound or mixtures of twoor more as above set forth. It will be appreciated that as theelectrolyte is used in plating, additions of the soluble mercurycompound must be made from time to time to maintain the desired mercuryconcentration.

With the desired mercury concentration in the plating bath, verysatisfactory copper plating will result when the bath is at anytemperature of from about 60 F. up to about 120 F. Excellent copperdeposits have been secured using baths operating at temperatures of fromabout F. to about F., which temperatures appear to define the optimumrange.

Current densities can be varied depending on the temperatureandconcentration of the bath. With bath agitation, current densities offrom about 10 to 200 amperes per square foot can be used and from about10 to 50 amperes per square foot without agitation. Control of currentdensity is within the skill of those versed in the art.

Aqueous acid copper electroplating electrolytes with the desired mercuryconcentration, with or without organic acids, dextrin, dextrose, or anyother known additive capable of extending the useful life of the bath orotherwise improving the copper electrodeposition, as will be set forthhereinafter, can be employed for plating metal by passing eithercontinuous direct-current or periodically reversed electrical current,or other suitable electrical current therethrough. Excellent resultshave been obtained with direct-current plating of such electrolytes.Periodic reverse current plating will give satisfactory electrodepositsalso.

Other plating current such as interrupted direct current and alternatingcurrent superimposed on direct current can be employed if desired.

Referring to the drawing, there is illustrated in FIG. 1 an apparatus 10for practicing the present invention. This apparatus comprises a tank 12provided with a suitable liner 14 of rubber, glass or the like,resistant to the acid electrolyte, carrying an electrolyte 16 composedof an aqueous solution of copper sulfate, sulfuric acid and the mercuryaddition agent of this invention alone or together with other knownaddition agents.

Disposed within the electrolyte 16 is an anode 18 that can be composedof copper or lead, or separate anodes of both. If lead anodes are used,the copper must be replenished by introducing copper sulfate into theelectrolyte 16 from time to time. The anode 1 8 is suspended by asupport 19' from a conductor bar 20. A member 22. to be plated withcopper is suspended by a support 24 from the second conductor bar 26.The conductor bars 20 and 26 are provided with electrical current from asuitable source 28 which can be a generator, a rectifier, storagebatteries, or the like. Electrical current passing from the source 28 tothe conductor bars 20 and 26 passes through the anode I 18. electrolyte16 and the member 22 to cause copper to structure. The electrodeposit isextremely bright if known brightening agents are used in conjunctionwith the mercury addition.

Copper can be plated from the above described electrolyte containing themercury addition in accordance with this invention by means of aperiodically reversed electrical current composed of cycles, each ofwhich passes electrical current through the member for a period of timeof from 0.01 second to 100 seconds to plate copper on the base memberand then the direction of flow of the current is reversed to deplate apart of the previously plated copper.

consists of smooth, dense, ductile copper upon which a second layer ofcopper is plated bythe plating portion of the next cycle of periodicreversed current and then a portion of this second increment is deplatedby passing deplating current leaving a second increment of stillsmoother copper than the first increment, and so on.

"Referring to FIGURE 2 of the drawing, a graph is shown illustratingonetype of periodic reverse current as it is applied to the base memberto be plated. Such periodic cycles can be produced by periodicallyreversing the flow of uniform direct current. base member when firstimmersed in the electrolyte is at a zero potential so that no currentflows when the first cycle of periodically reversed current is: applied,a cathodic or plating current of a density of the value of A is appliedand metal is plated for a period of time X to a point B, then thedirection of flow of the current is reversed so that the current densityin the member drops frorn'the value B to zero and then becomes anodicand will deplate copper, reaching a deplating current density of C.Metal is deplated for a period of time Y, which is about at leastone-twelfth of the length of period X, at the current density of C to Duntil sufiicient coulombs of deplating current have been applied to thecoulombs of from 8% to 90% of the coulombs applied during the platingperiod X. The cycle A-BC-D deposits an increment of sound, smooth copperbase. The direction of current flow is again reversed from D throughzero and then plating current of a density value of F is applied tobegin another cycle which will plate ,a second increment of copper.

It will be understood that the showing in FIGURE 2 is merely schematicand that the current density is not necessarily uniform from A to B or Cto D as shown, but will usually vary and be relatively non-uniform.Also, in reversing from B to C and from D to F, the time required isfinite and these lines will not be vertical, as shown, but will take anappreciable period of time, depending upon the various factors involvedin the plating installation. The deplating or anodic current density C-Dcan be equal to the plating current density-A-B, or exceeded or can beas low as 8% of the plating current density. Reference should be had toPatents 2,451,341;

2,678,909 and 2,470,775 for additional information as to periodicreverse current cycles.

In order to indicate more fully the advantages and capabilities of thepresent invention, the following specific examples are set forth toillustrate the utilization of the mercury addition agent of thisinvention in acid electrolyte plating baths.

It is assumed that the Example 111 An aqueous electroplating electrolyteof the following composition is prepared:

Ounces per gallon of electrolyte Copper sulfate (crystals) [CuS0 .5H O]28 Sulfuric acid (98%) 8 Mercuric sulfate 0.005 Hydrochloric acid (37%)0.006

This bath is operated at various temperatures from about 60 F. to about120 F. with satisfactory results. Temperatures of from about F. to about100 F. appear to give optimum plating results.

Copper is plated from the bath of this Example III on rectangular brasspanels using direct current at a current density of about 50 amperes persquare foot and at a temperature of about F. Copper is deposited untilthere is applied to the rectangular brass panel copper plate of athicknessof about 3 mils. The copper plate has relatively goodductility, is a smooth and fine grained copper deposit and has arelatively high density.

Example IV The following electrolyte is prepared:

Ounces per gallon of electrolyte Copper sulfate (CuSO 5H O) 28 Sulfuricacid (98%) 8 HQ (37%) 0.006 P-acetoxymercuric aniline 0.05

Copper is plated from this bath on rectangular brass panels using directcurrent at a current density of about 60 amperes per square toot and ata temperature of about 90 F. Copper is deposited on the panel to athickness of about 4 mils. The copper plate has good ductility, is finegrained and smooth.

Example V The following electrolyte is prepared:

Ounces per gallon of electrolyte Copper sulfate (CuSO .5H O) 28 Sulfuricacid (98%) 8 HCl (37%) 0.006 Mercurous sulfate 0.007

Copper plated on a brass panel from the bath is ductile, smooth and finegrained.

When direct current is applied to the electrolyte, excellent deposistsof copper are produced on base members at current densities of fromabout 5 to 200 amperes per square foot. The copper deposit is extremelybright, smooth, fine grained, dense and has good ductility.

The addition of certain water soluble carboxylic acids, dextrin, ordextrose to acid copper electrolyte baths containing the soluble mercuryadditive of this invention and the known primary brightening agentsenables the addition agents to function under maximum efliciency forlonger periods of time than is normally possible. Citric acid, malicacid, maleic acid, linoleic acid, adipic acid, aconitic acid, and oxalicacid are examples of acids that can be employed for this purpose. Any ofthese or mixtures of two or more are employed in amounts of from 0.001ounce up to about 3 ounces per gallon of electrolyte Ounces per gallonof electrolyte Copper sulfate (crystals) [CuSO .5H O] 28 Sulfuric acid(98%) 8 Mercuric sulfate 0.01 Hydrochloric acid (37%) 0.006 Dextrin(yellow) 0.008

The copper deposits obtained using this electrolyte at a bathtemperature of about 80 F. are fine-grained and ductile at currentdensities of from to 120 amperes per square foot.

Example VIII The following electrolyte is prepared:

Ounces per gallon of electrolyte Copper sulfate (crystals) [CuSO .5H O]28 Sulfuric acid (98%) 8 P-acetoxymercuric aniline 0.05 Citric acid 0.25Reaction product of 1-acetyl-2-thiohydantoin and monoethanolamine 0.001

The copper deposits obtained using this electrolyte are ductile, smoothand have a high luster.

Example IX The following electrolyte is prepared:

Ounces per gallon of electrolyte Copper sulfate (crystals) [CuSO .5H O]28 Sulfuric acid (98%) 8 Mercuric sulfate 0.01 Hydrochloric acid (37%)0.003 Dextn'n 0.004 l-acetyl-Z-thiohydantoin 0.01

Copper electrodeposited from this bath is very bright, smooth andductile.

Example X The following electrolyte is prepared:

Ounces per gallon Copper sulfate (crystals) [CuSO .5H O] 28 Sulfuricacid (98%) 8 P-acetoxymercuric aniline 0.05 Citric acid 0.25

Reaction product of 2-thiohydantoin and pyridine 0.001

The copper electrodeposits obtained by using this bath or electrolyteare ductile, smooth, and of high luster.

Example XI The following electrolyte is prepared:

Ounces per gallon Copper sulfate (crystals) [CuSo .5H O] 28 Sulfuricacid (98%) 8 Mercuric sulfate 0.01 Hydrocholoric acid (37%) 0.003Dextrin 0.004 Reaction product of Z-thiohydantoin and methanediamine.002

When direct current is applied to the electrolyte, excellent copperelectrodeposits are produced on base members at 10 current densities offrom 5 to 200 amperes per square foot.

While the present invention has been described with particular referenceto preferred embodiments thereof, it will be understood, of course, thatcertain changes, substitutions, modifications and the like may be madetherein without departing from the scope thereof.

I claim as my invention:

1. An aqueous electrolyte plating solution comprising copper sulfate,sulfuric acid, and a water soluble mercury compound in an amountsufficient to provide mercury in the range of from about 0.0003 to 0.01ounce per gallon in solution in said bath.

2. An aqueous electrolyte plating solution comprising copper sulfate,sulfuric acid and an amount of mercury in the range of from about 0.0003to 0.01 ounce per gallon in solution in said bath, said mercury beingintroduced into the bath in the form of soluble compounds of mercury.

3. An aqueous electrolyte plating solution comprising copper sulfate,sulfuric acid, from 0.001 to 0.06 ounce of chloride ion per each gallonof electrolyte, and a Water soluble mercury compound in an amountsufiicient to provide mercury in the range of from about 0.0003 to 0.01ounce per gallon in solution in said bath.

4. An aqueous electrolyte plating solution comprising copper sulfate,sulfuric acid, from 0.0005 to 0.05 ounce per gallon of at least oneZ-thiohydantoin compound, and a water soluble mercury compound in anamount sufiicient to provide mercury in the range of from about 0.0003to 0.01 ounce per gallon in solution in said bath.

5. An aqueous electrolyte plating bath comprising copper sulfate,sulfuric acid, a water soluble mercury compound in an amount sufficientto provide mercury in the range of from about 0.0003 to 0.01 ounce pergallon in solution in the bath, and from 0.0001 to 0.5 ounce per gallonof the product obtained by admixing and heating substantially equimolarquantities of at least one compound having the nucleus II I ll with atleast one compound selected from the group consisting of (A) monocyclicunsubstituted aromatic compounds containing in the ring structure from 4to 6 carbon atoms and from 1 to 2 nitrogen atoms per molecule, (B)compounds having the formula wherein R is a radical selected from thegroup consisting of hydrogen, phenyl radicals, aminophenyl radicals,monovalent and divalent saturated aliphatic hydrocarbon radicals havingfrom 1 to 4 carbon atoms and in which the substituents are -NH radicals,monovalent and divalent alicyclic radicals containing from 5 to 6 carbonatoms in the ring in which the substituents are selected from the groupconsisting of CH and -NH radicals, and monovalent and divalentheterocyclic radicals having from 5 to 6 carbon atoms in the ring and inwhich hereto atoms occur only in the ring structure and the substituentsoccur only in the carbon atoms and are NH radicals, and (C)alkylolamines in which the groups substiuted on the nitrogen atoms areselected from the group consising of hydrogen, alkyl groups, and alkylolgroups having from 1 to 4 carbon atoms, there being at least one alkylolgroup per molecule.

6. An aqueous electrolyte as set forth in claim 5 which contains from0.001 ounce to 3 ounces of at least one Water soluble carboxylic in eachgallon of the electrolyte.

7. An aqueous electrolyte as set forth in claim 5 which contains from0.001 ounce to 5.0 ounces of dextrin in each gallon of electrolyte.

8. An aqueous electrolyte as set forth in claim 5 which 1 1 containsfrom 0.001 ounce to 5.0 each gall-on of electrolyte.

9. In the process of plating copper on a base member from an acidelectrolyte having an anode therein, said electrolyte comprising coppersulfate and sulfuric acid, the steps comprising adding a soluble mercurycompound to the electrolyte in an amount sutiicient to provide an amountof mercury in the range of from about 0.0003 to 0.01 ounce per gallon insolution in said bath, and then passing a plating electrical currentfrom the anode through the electrolyte and to the member to depositcopper on the member.

10. The process of claim 9 in which there is from 0.001 to 0.06 ounce ofchloride ion in each gallon of the electrolyte.

11. The process of claim 9 in which there is from 0.0005 to 0.05 ounceper gallon of at least one 2-thiohydantoin compound in each gallon ofthe electrolyte.

12. The process of claim 9 in which there is present in an amount equalto from about 0.0001 to 0.5 ounce per gallon, the product obtained byadmixing and heating substantially equimolar quantities of at least onecompound having the nucleus ounces of dextrose in with at least onecompound selected from the group consisting of (A) monocyclicunsubstituted aromatic compounds containing in the ring structure from 4to 6 carbon wherein R is a radical selected from the group consisting ofhydrogen, phenyl radical, aminophenyl radicals and divalent saturatedaliphatic hydrocarbon radicals having from 1 to 4 carbon atoms and inwhich the substituents are NH radicals, monovalent and divalentalicyclic radicals containing from 5 to 6 carbon atoms in the ring inwhich the substituents are selected from the group consisting of CH;,and NH radicals and monovalent and divalent heterocyclic radicals havingfrom 5 to 6 carbon atoms in the ring and in which hetero atoms occuronly in the ring structure and the substituents occur only on the carbonatoms and are NH radicals, and (C) alkylolamines in which the groupssubstituted on the nitrogen atom are selected from the group consistingof hydrogen, alkyl groups, and alkylol groups having from 1 to 4 carbonatoms, there being at least one alkylol group per molecule.

13. The process of claim 9 in which there is present dextrin in anamount equal to from about 0.001 ounce to 5.0 ounces per each gallon ofthe electrolyte.

14. The process of claim 9 in which there is present dextrose in anamount equal to from about 0.001 ounce to 5.0 ounces per each gallon ofelectrolyte.

15. In the process of plating copper on a base member from an acidelectrolyte having an anode therein, said electrolyte comprising coppersulfate and sulfuric acid, the steps comprising adding a soluble mercurycompound to the electrolyte in an amount suflicient to provide an amountof mercury in the range of from about 0.0003

to 0.01 ounce per gallon in solution in said bath, and then passingcycles of periodically reversed electrical current through the basemember, the aqueous electrolyte, and an anode, each cycle of currentfirst flowing in one direction to plate copper on the basefor a periodof from 0.01 second to 100 seconds, then the direction of current flowreversing for a period of time to deplate a portion of the previouslyplated copper, the coulombs applied during the deplating period equal tofrom 8% to of the coulombs applied during the plating period, theplurality of cycles of periodically reversed current electroplatingsmooth sound copper on the base.

16. The process of claim 15 in which there is from 0.001 to 0.06 ounceof chloride ion in each gallon of the electrolyte.

17. The process of claim 15 in which there is from 0.0005 to 0.05 ounceper gallon of at least one 2-thiohydantoin compound in each gallon ofthe electrolyte.

18. The process of claim 15 in which there is present in an amount equalto from about 0.0001 to 0.5 ounce per gallon of electrolyte the productobtained by admixing and heating substantially equimolar quantities ofat least on compound having the nucleus with at least one compoundselected from the group consisting of (A) monocyclic unsubstitutedaromatic compounds containing in the ring structure from 4 to 6 carbonatoms andfrom 1 to 2 nitrogen atoms per per molecule, (B) compoundshaving the formula wherein R is a radical selected from the groupconsisting of hydrogen, phenyl radical, aminophenyl radicals, monovalentand divalent saturated aliphatic hydrocarbon radicals having from 1 to 4carbon atoms and in which the snbstituents are NH radicals, monovalentand divalent alicyclic radicals containing from 5 to 6 carbon atoms inthe ring in which the substituents are selected from the groupconsisting of CH and NH radicals, and monovalent and divalentheterocyclic radicals having from 5 to 6 carbon atoms in the ring and inwhich hetero atoms occur only in the ring structure and the substituentsoccur only on the carbon atoms and are NH radicals, and (C)alkylolamines in which the groups substituted on the nitrogen atom areselected from the group consisting of hydrogen, alkyl groups, andalkylol groups having from 1 to 4 carbon atoms, there being at least onealkylol group per molecule.

19. The process of claim 15 in which there is present dextrin in anamount equal to from about 0.001 ounce to 5.0 ounces per each gallon ofelectrolyte.

20. The process of claim 16 in which there is present dextrose in anamount equal to from about 0.001 ounce to 5.0 ounces per each gallon ofelectrolyte.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN AQUEOUS ELECTROLYTE PLATING COMPRISING COPPER SULFATE, SULFURICACID, AND A WATER SOLUBLE MERCURY COMPOUND IN AN AMOUNT SUFFICIENT TOPROVIDE MERCURY IN THE RANGE OF FROM ABOUT 0.0003 TO 0.01 OUNCE PERGALLON IN SOLUTION IN SAID BATH.